Patent GB-1104041-A (GB)
Title: Wavefront reconstruction using a coherent reference beam
IPC: G02B27/00
Filed: 1965-03-22
Abstract: 1,104,041. Making holograms. BATTELLE DEVELOPMENT CORPORATION. March 22, 1965 [April 23, 1964], No. 12034/65. Heading G2C. A method of lenslessly producing images comprises directing a beam of coherent radiation from a source on to an object; positioning a detector to receive the reflected radiation from the object, which reflected radiation interferes with a portion of the coherent beam directed on to the detector after by-passing the object; and treating the detector so that at least one image of the object is recorded thereby. When the detector is a photographic plate, the wavelength of the radiation used lies between 10<SP>-11</SP> cms. and 10<SP>-1</SP> cms., a laser preferably being used to produce coherent radiation in the visible spectrum. In Figs. 7, 9 a two-beam inter-ferometric process is used to produce a hologram on a photographic plate 33. Part of an incident beam 23 of light from a laser 21 passes through a diffusion screen 28 and a transparent object 25 producing a beam 29 of scattered light carrying the Fresnel diffraction pattern of each point of the transparency 25. Part of the beam 23 by-passes the transparency and is deflected by a prism 27 to produce a reference beam 31. The beams 29, 31 interfere, the interference pattern being recorded on the plate 33, which is then developed. When the developed plate is illuminated with coherent light Fig. 8 (not shown) a real and a virtual image (not shown) are formed one each side of the plate in the axis of the beam. The plate also acts as a diffraction grating producing a first order pair of diffracted waves which in turn produce a real image (37) and a virtual image (35) in off-axis positions. In Fig. 9 an opaque object is illuminated with the beam 23, the reference beam 41 being reflected by a mirror on to the plate where it interferes with an information carrying beam 39 reflected by the object. After the plate is developed, a reconstruction is formed as before. The method can be embodied in a lensless microscope Figs. 10, 11(not shown) by illuminating the object with a diverging beam of coherent light, thus producing a diverging information carrying beam (51) and diverging reference beam (55) the interference patterns of which are captured on a plate (53). The developed plate is also illuminated with a diverging beam. In another embodiment Fig. 12 (not shown), a number of images from different objects may be put on a single photographic plate, each image being obtained by deflecting the part of the beam (63) used to obtain the reference beam through a different angle. When the developed plate is illuminated, the off-axis real and virtual images will be positioned in accordance with the angles through which the beam (63) was deflected in their formation Fig. 13 (not shown). The method of Fig. 12 may be applied to produce images in colour, using black and white photo-sensitive material Figs. 14-16, (not shown). Three sources, a red laser (101), a yellow laser (103) and a blue laser (105) are positioned to illuminate the object. Prisms (111), (115), (119) which each pass light of one colour only, are arranged to deflect the reference beams (125), (129), (13#) on to the plate (121) where they interfere with the information carrying beams (123), (127), (131) respectively, each pair of beams producing an interference pattern each orientated in a separate way on the plate. If the object is replaced by an opaque screen, a three dimensional image (if the object is three dimensional) is formed on the axis, the virtual image lying between the plate and the screen. This method may be modified for use with an opaque object and mirrors. An on-axis image in colour will be formed as long as the illuminating beams are inclined to the complex hologram at the same angles as the reference beams were inclined to the plate. In both cases, six other off axis images appear (Fig. 15). If light is passed directly to the complex hologram from the three lasers, nine images are formed (Fig. 16). In a further embodiment, Figs. 17, 18 (not shown) the method is used to make an optical system (169) connect itself by making a hologram of the system, including its aberrations, and then using the hologram (177) as a diffraction grating to produce a highly connected system.